1. Field of the Invention
The present invention relates to a vehicular rotary electric machine, such as an AC generator for example, that is mountable on cars and trucks.
2. Description of Related Art
Generally, many cars are being designed with slanting hoods to minimize aerodynamic drag. Additionally, cars are also being designed with smaller engine compartments in order to provide greater interior space. As a result, there is increasingly less space available for mounting AC generators within the vehicle engine compartments. Meanwhile, increasingly lower engine revolutions (rpm) achieve increasingly better fuel economy, but reducing engine rpm also reduces the rpm of the vehicular AC generator. On the other hand, the need for increasingly higher power outputs of vehicular AC generators are increasingly greater because of the increased electrical loads created by controllers of safety features and other electrical loads. Thus a small high-power and low-cost vehicular AC generator is in great demand.
Another problem is that fan noise and magnetic noise of a supplementary machine such as the vehicular AC generator, which is driven at a relatively high speed, has become more and more bothersome. This is because engine noises have been greatly reduced in recent years in response to social demands for less traffic noise and in order to enhance commercial value of cars by making the interiors more quiet. A typical stator winding used in a conventional vehicular AC generator adopts a structure in which continuous wires are wound around a stator core. Additionally, various improvements to the stator windings have been proposed to meet the above-described demands of compactness, high power output, and low noise.
For example, Japanese Patent Laid-Open Publication No. Sho 54-66406 discloses inserting a collective winding successively into the slots of the stator from outer layers, so as to prevent the stator winding from crossing at one coil end and becoming long. With this structure, however, although the wires do not cross each other at one coil end as they are inserted from outer layers towards inner layers of the slots in succession, there arises another problem in that there is a dead space within the slots since the outer layers of the winding are arranged on the outer side and the inner layers on the inner side in the slots. On the other hand, an attempt to fill the slots with coils so as not to leave any dead space would result in the wire layers crossing each other between the inside of the slots and the coil end.
To overcome the problem of intersection of the winding at the coil end and within the slots, Japanese Patent No. 2927288 proposes a technique which adopts a stator winding constructed of a plurality of conductor segments in order to increase the space filling factor of the stator winding within the slots and to ensure high cooling efficiency on the outside of the slots by cooperation with the rotor. With this structure, the ends of a plurality of conductor segments are bonded together by welding to form a stator winding. The bond areas are therefore heated to a high temperature during the welding, and so is the vicinity of the bond areas because of the heat conduction. As a result, the insulation films near the bond areas become deteriorated by the heat stress, and the lessened adhesion of the films to the conductors result in peeling and cracking in the films. Conductor segments with peeled or cracked insulation film may cross each other and cause short circuits, since they are in close proximity to each other. Car vibrations and the like can also bring about short-circuiting across the conductor segments at the coil end near the bond areas because the insulation film may become damaged by friction or mechanical shock due to the contact.
In view of these problems, the applicant of the present invention has proposed, in Japanese Patent Laid-Open Publication No. 2000-166148, a technique to provide clearances between the conductor segments that radially adjoin and intersect each other at the coil end by forming radial indentations in the conductor segments at the intersecting points. The cross-sectional area of the conductor segment remains unchanged even in the indentation, since the corner radius of the rectangular cross section of the conductor segment is large enough to absorb the displacement of material when forming the indentation by pressing. In other words, the clearance provided by the formation of the indentation is defined by the corner radius of the rectangular cross section and the width of the conductor segment.
However, the design disclosed in Japanese Patent Laid-Open Publication No. 2000-166148 has the problem that, under the condition that the cross-sectional area of the conductor segment should remain the same before and after the formation of the indentation, the size of the indentation (or the depth of the indentation) becomes smaller in proportion to a decrease in the corner radius of the rectangular cross section, or to an increase in the width, of the conductor segment. If the clearances are not sufficiently large between crossing conductor segments, the insulation film may become particularly susceptible to damage by the friction or the mechanical shock due to the contact which may cause short-circuiting to occur.